Dewaxing of mineral oils



March 2, 1965 RQA. wooDLE DEwAxING QFMNERAL oILs Filed Mw. 29, 1960 United States Patent O 3,171,798 DEWAXING F MINERAL OILS Robert A. Woodle, Nederland, Tex., assignor to Texaco Inc., New York, NX., a corporation of Delaware Filed Nov. 29, 1960, Ser. No. '72,403 3 Claims. (Cl. 208-33) This invention relates to the manufacture of a lubricating oil from petroleum oil, and, more particularly, relates to the manufacture of low pour test lubricating oil from wax-bearing mineral oil.

Most types of petroleum crude oil, and particularly parainic crudes, contain at least small quant-ities of waxes. Upon distillation, for example, these waxes are carried into the distillate fractions. When a petroleum fraction containing wax is used as a lubricant base, the waxes present in the oil fraction crystallize out at low temperatures, and therefore interfere with the ow or circulation of the oil. Many applications therefore require that the wax content of the oil be reduced to a minimum or be substantially eliminated.

The conventional practice of dewaxing a mineral oil fraction involves chilling the oil to a sufficient temperature to cause solidication of the wax. The wax-bearing mineral oil to be treated is advantageously admixed with a selective solvent which shows a preferential solubility for oil over wax at the low temperature or dewaxing temperature. The solvent employed is fluid at this low temperature and reduces the viscosity of the oil to such an extent that low temperatures may be employed in dewaxing. The resulting admixture is cooled to the desired dewaxing temperature to crystallize the wax which is then separated by filtration, centrifuging or the like. The pour point of the oil produced by this process may be as low as F., or slightly lower. However, wax removal is not complete and many applications require a pour point lower than that obtained by solvent dewaxing.

It is an Object of this invention to produce a lubricating oil having a substantially lower content of wax than that obtained by conventional solvent dewaxing alone.

It is another object of this invention to provide an improved dewaxing process involving dewaxing mineral oil from a cold solution thereof and treating the filtrate resulting therefrom to render a substantially wax-free lubricating oil of low pour point.

It is still another object to provide a process of the above type which involves contacting the ltrate resulting from the solvent dewaxing process with activated carbon to further reduce the wax content of the mineral oil, and which involve regenerating the activated carbon with the same solvent employed in the solvent dewaxing process.

In carrying out the process of my invention, a waxbearing mineral oil is admixed with a solvent and the resulting mixture chilie/ to a dewaxing temperature to crystallize and precipitate the wax. The oil-solvent mixture generally 4is cooled to a temperature that is about 15 F. lower thatn the pour point sought in the product. Usually the dewaxing temperature is in the range of from about 0 F. to 30 F., and therefore for an oil of 0 F. pour point, for example, the dewaxing temperature is about -15 F. rlhe crystallized wax is removed by ltration, centrifuging, decanting or the like, and the resulting wax cake may be washed with additional solven-t to remove any retained oil. The wax cake may be passed to a recovery unit to remove occluded materials and to recover the wax by-product.

In accordance with my invention, the solution remaining upon separation of the solidified wax, i.e., the filtrate, comprising oil of low wax content and solvent is brought into intimate ycontact with activated carbon in particulate form at a temperature of from about F. to about ll Patented Mar. 2, i955 300 F., and preferably at a temperature of from about to about 200 F. A bed of activated carbon advantageously may be saturated with the oil-solvent solution, and the solution percolated through the bed as in a column. Wax dissolved in the oil-solvent solution and not removed by the chilling step is adsorbed by the activated carbon. Employing a temperature lower than the described minimum retards adsorbtion of the waxy constituent by the activated carbon. On the other hand, temperatures in excess of the described range result in loss of product, and further may cause undesirable side reactions. Although the pressure employed in the process is not particularly critical, it is generally convenient and economical to conduct the process at atmospheric pressure. Where desired, higher pressures may be used to increase the rate of iow of product through the carbon bed. The oilsolvent solution is contacted with the activa-ted carbon for a length of time sufficient to achieve the desired pour point in the nal product which is somewhat dependent upon the percentage of wax present. Generally, a rate from about 0.1 to 10 barrels of solution pe-r hour per ton of activated carbon is satisfactory. The treated solution comprising oil and solvent is withdrawn from contact with the activated carbon, and the resulting solution then passed to a recovery unit to recover separately the solvent and an oil product substantially free of waxy constituents. The oil product, characterized by a low pour point, possesses superior lubricating properties. An oil product obtained from a parafnic crude when treated in accordance with our process, exhibits a pour point usually not less than about 10 F., and preferably 20 F., lower than that achieved by conventional solvent dewaxing from a cold admixture of oil and wax.

As the carbon adsorption step continues, the adsorbtive capacity of the carbon decreases until the oil product fails to meet the desired pour test. At this point, passage of the solution of oil and solvent through the activated carbon is interrupted, and the carbon is regenerated. In regenerating the spent carbon, at least part o-f the same solvent employed in the process and subsequently recovered is passed through the spent bed of carbon. The temperature of the solvent is generally at about room. temperature or slightly above, and preferably is in the range of from about 70 to 200 F. The amount of solvent required in regenerating the carbon is a function of the solubility of the wax adsorbed by the carbon in the solvent. Usually more than about 5 barrels of solvent per ton of carbon are required, and preferably more than about l0 barrels of solvent, suitably 10 to 50 barrels per ton `of carbon are employed for regeneration. The solvent is advantageously passed through-the carbon bed at a rate of about 0.5 to 15 barrels of solvent per hour per ton of carbon, preferably about 3 to l0 barrels. Upon completion of the regeneration step, the carbon is ready for use in contacting additional oil undergoing dewaxing.

The resulting solution comprising the desorbed wax and solvent may be returned to the cooling step of the solvent dewaxing operation where this solution is conibined with additional mineral oil being fed to the operation.

The solvent used in carrying out the process is of the selective type having a substantially complete solvent action upon the mineral oil but substantially no solvent action upon the wax at such temperatures employed in dewaxing from chilled solutions. Such a solvent cornprises, for example, a mixture of an aliphatic ketone, such as acetone, methylethyl ketone or methyl isobutyl ketone, and an aromatic hydrocarbon, such as benzene, toluene, or a mixture of benzene and toluene. It is contemplated, however, that mixtures of other aliphatic ketones and aromatic hydrocarbons may be employed, or that the aromatic hydrocarbon may be employed by itself. Such solvents as low-boiling petroleum hydrocarbons, including" naphtha, gasoline, pentane, etc. or mixtures thereof, may be used, as may certain hydrocarbon derivatives such as chloroform or ether.

This invention is particularly adapted to the dewaxing of wax-bearing mineral oil derived from paraffin base crudes, examples of which include Pennsylvania, East Texas, Rhodesia, paratiinous Venezuelan, etc. Such crudes contain about 5 to 50% of wax by volume of the oil.

To further illustrate the operation of the invention, the following speciiic example is provided which should be read with reference to the accompanying drawing showing a ow diagram of the present process.

A wax-bearing mineral oil having a Saybolt Universal viscosity of about 85 to 95 seconds at 100 F. and containing about 8 to 10% wax by volume, is introduced from a source not shown through conduit 2 leading to a chiller 6. A solvent liquid consisting of a mixture of about 50% methylethyl ketone and 50% toluene is recycled from a recovery source, describedkin greater detail hereinbelow, and passed through pipe 4 into the oil charge. The oil and solvent are mixed in the proportion of about 1 part of oil to about 3 parts of solvent per volume. The resulting mixture passes to the chiller 6 where itis chilled to a temperature of about 15 F. in orde-r to precipitate the wax and produce a lubricating oil of about 0 F. pour test.

From the chiller, the cold mixture passes to a iilter 10 wherein the solid wax is removed as a ilter cake, producing a ltrate comprising oil and solvent which is drawn off through conduit 14. The resulting ilter cake may be washed in situ with fresh solvent introduced via line 11 (from a source not shown). The resulting ilter cake, containing small quantities of occluded oil and solvent not removed by the washing step, is discharged into recovery unit 12 wherein the solvent may be recovered and 'reused in the process and the wax passed to storage.

The filtrate passes through conduit 14 to a reversing valve 16. With the valve in the position shown by the *solid line, the filtrate passes through line 18 and into bed 20 of activated carbon. The filtrate may be heated either prior to passage to the carbon bed, or after contact with the carbon, by a suitable heat exchanger (not shown). The ltrate is percolated through ybed 20 at a temperature of about 100'o F. and a rate of about 7 barreis per ton of carbon per hour such that wax not removed from the chilled mixture in the chiller 6 is absorbed by the activated carbon, and the resulting solution containing dewaxed oil in solvent is discharged through conduit 22 to a reversing valve 24. With the valve in the position indicated by the solid line, the resulting solution is directed through line 26 to recovery unit 28 to recover separately the solvent and dewaxed oil. The dewaxed product removed through line 29 showed a pour point of F.

Y The process advantageously employs two or more carbon beds such that dewaxing treatment may be carried out in one bed while the second bed is being regenerated for subsequent use with additional feed. In regenerating the spent carbon, the solvent recovered in unit 28 is passed through line 30 to reversingvalve 16 which is in the position shown by the solid line. The solvent then passes through line .32 and into bed of spent carbon at a temperature of about 100 F. and at a rate of about'12 barrels of solvent per hour per ton of carbon. The wax desorbed from the carbon and solvent are discharged through conduit 34 to a reversing valve 24 open to the position shown by the solid line, and the solution recycled to chiller 6 vialines 36 and 4.

When the carbon bed 20 has become spent, the valves 16 and 24 are switched to the position shown by the dotted lines. With the valves in this position, the oilsolvent mixture from line 14 is directed through line 32 and into carbon bed 20'. The treated mixture of dewaxed oil and solvent is then passed to recovery unit 28 via conduits 34 and 26. Similarly, the solvent recovered from unit 28 is passed to bed 20 to regenerate the carbon via conduits 30 and 18. Ther solvent containing wax dissolved therein is then passed through lines 22 and 36, and Yrecycled in further operation of the process.

The following example will further illustrate the nature of this invention. A paran base oil distillate derived from a Texas crude was solvent dewaxed. froma cold solution to a pour point of 0 F. 12 pounds of activated carbon were charged to a 6 footV steel tower having a 4 inch inside diameter, and provided with a surrounding jacket to control the operating temperature. The oil distillate was dissolved in a solvent comprising equal parts of methylethyl ketone and toluene in the ratio of 2 parts of solvent to 1 part of oil. The oil-solvent mixture was charged to the carbon bed at room temperature and at a charge rate of7 barrels of mixture per ton of carbon per hour. The iinal oil product drawn from the bed had a pour point of 25 F.

The spent carbon was regenerated by washing it with the same solvent recovered in the process at a rate of 11 barrels of solvent per ton of carbon per hour and at room temperature. 18 barrels of solvent per uton of carbon were used in the regeneration step. Additional oil to be treated was charged to the regenerated carbon bed as above, and the iinal oil product showed a pour point of 15 F.

Reference has been made to the dewaxing solvent mixture of Amethylethyl ketone and toluene. Other solvents, including mixtures of compounds, are also contemplated as explained above in detail. The solvent ratios, as set forthY above in the specific examples, may vary widely in accordance with known practice, depending upon the nature and source of the wax-bearing mineral oil undergoing treatment and the solvent employed. I claim:

1. In the production of a low pour test lubricating oil from a wax-bearing mineral oil by steps comprising mixing said mineral oil with a solvent having substantially cornplete solvent action upon said mineral oil, chilling the resulting mixture to a dewaxing temperature to crystallize the wax, removing the crystallized wax from the remaining mixture comprising oil, dissolved wax, and solvent, and then recovering oil and solvent separately from said remaining mixture, the improvement which comprises contacting said remaining mixture with a bed of activated carbon etfecting removal of dissolved wax therefrom not removed by said chilling step at a temperature of from about 30 to 300 F., said activated carbon having afiinity for said wax, and contacting the carbon spent by reason of the wax removal step with at least a portion of said recovered solvent at a rate of 0.5 to 15 barrels of solvent per hour per ton of carbon and .at a temperature of about 70 to 200 F. to dissolve and remove wax adsorbed by said activated carbon.

2. In the production of a low pour test lubricating oil from a wax-bearing mineral oil stock by the steps comprising mixing said mineral oil stock with a solvent having substantially complete solvent action upon said mineral oil, chilling the mixture to a dewaxing ltemperature to crystallize the wax, filtering the chilled mixture toA produce a ltrate comprising oil, dissolved wax, and solvent and a lter cake of wax, and then separating the oil from the solvent, the improvement which comprises contacting said filtrate with a lbed 'of activated carbon effecting removal of dissolved wax therefrom at a temperature of from about 70 to 200 F., and at a charge rate of 0.1 to 10 barrels of filtrate per hour per ton of carbon, said activated carbon having aflinity for said wax, and contacting the carbon upon becoming spent with at least a portion of said recovered solvent at a rate of 0.5 to 15 barrels of solvent per hour per ton of carbon to dissolve and remove wax adsorbed by said activated carbon at a temperature,l of from about 70 to 200 F.

3. In the production of a low pour test lubricating oil from a Wax-bearing mineral oil by the steps comprisingr mixing said mineral oil with a solvent having substantially complete solvent action upon said mineral oil at dewaxing temperature, chilling the mixture to a dewaxing temperature to crystallize the Wax, filtering the chilled mixture to produce a ltrate comprising oil, dissolved wax, and solvent and a lilter cake of Wax, and then recovering separately from said ltrate the oil and solvent, the improvement which comprises contacting said filtrate with a bed of activated carbon eifecting removal of dissolved Wax therefrom at a temperature of from about 30 to 300 F., said activated carbon having ainity for said Wax, contacting the carbon upon becoming spent with at least a portion of said recovered solvent at a rate of 3 to 10 barrels of solvents per hour per ton of carbon to dissolve and remove wax adsorbed by said activated carbon, and adding the resulting solution containing desorbed Wax and solvent to the chilling step in further operation of the process.

References Cited in the lile of this patent UNITED STATES PATENTS 10 2,300,420 Hassier et ai Now/.3,1942 2,581,573 Biles et al Ian. 8, 1952 2,754,250 Shipman July 10, 1956 

1. IN THE PRODUCTION OF A LOW POUR TEST LUBRICATING OIL FROM A WAX-BEARING MINERAL OIL BY STEPS COMPRISING MIXING SAID MINERAL OIL WITH A SOLVENT HAVING SUBSTANTIALLY COMPLETE SOLVENT ACTION UPON SAID MINERAL OIL, CHILLING THE RESULTING MIXTURE TO A DEWAXING TEMPERATURE TO CRYSTALLIZE THE WAX, REMOVING THE CRYSTALLIZED WAX FROM THE REMAINING MIXTURE COMPRISING OIL, DISSOLVED WAX, AND SOLVENT, AND THEN RECOVERING OIL AND SOLVENT SEPARATELY FROM SAID REMAINING MIXTURE, THE IMPROVEMENT WHICH COMPRISES CONTACTING SAID REMAINING MIXTURE WITH A BED OF ACTIVATED CARBON EFFECTING REMOVAL OF DISSOLVED WAX THEREFROM NOT REMOVED BY SAID CHILLING STEP AT A TEMPERATURE OF FROM ABOUT 30* TO 300*F., SAID ACTIVATED CARBON HAVING AFFINITY OF SAID WAX, AND CONTACTING THE CARBON SPENT BY REASON TO THE WAX REMOVAL STEP WITH AT LEAST A PORTION OF SAID RECOVERED SOLVENT AT A RATE OF 0.5 TO 15 BARRELS OF SOLVENT PER HOUR PER TON OF CARBON AND AT A TEMPERATURE OF ABOUT 70* TO 200*F. TO DISSOLVE AND REMOVE WAX ADSORBED BY SAID ACTIVATED CARBON. 